1. Field of the Invention
The invention relates broadly to medico-surgical tube structures and methods of their manufacture. More particularly, it concerns methods for finishing the distal ends of medico-surgical tubes, especially catheters.
2. Description of the Prior Art
Catheter distal end tips should not have sharp corners, sharp points, ragged edges or any other injury causing features. Manufacturers have either hand finished or molded the tips to eliminate such problems. Molding in heated cavities has become the common method (see U.S. Pat. No. 3,725,522).
One problem associated with the molding method is the trapping of air in and around the molten plastic at the bottom of the heated mold. As the tube is forced down into the mold, air becomes compressed ahead of it much the same as a piston being forced into a cylinder. If there is no means for the air to escape, it prevents the plastic from taking the shape of the mold, or some air may become trapped within the plastic as a bubble or blister.
Two methods are commonly used to deal with the air trapping problem. One is to provide a bleed hole to let the air escape (see U.S. Pat. Nos. 3,725,522 and 4,292,270). A second is to provide enough clearance around the tube and the mold cavity so air can escape back up the cavity. However, by doing either of these, new problems can be created.
In the bleed hole method, while the hole allows the softened plastic to take the shape of the mold, some plastic may be extruded through the bleed hole. When the tube is then removed from the mold, it is left with a projection or other evidence where the bleed stringer has broken off. If the second method is used, it is possible that the molten plastic can be forced back up the clearance space. This can produce a flap or ridge which is undesireable.